A high-speed and large-capacity transmission technique is necessary with the recent rapid increase in the demand for wireless communication. In order to realize size reduction and high performance of a filter, expectations have been raised due to the practical use of a microstrip line superconductor filter using a high-temperature superconductor as a wiring material. A superconductor has an extremely small surface electric resistance even in a high frequency region, such as microwave, as compared to a normal electrically good conductor. Therefore, when the superconductor is used in a filter with a plurality of resonator patterns arranged on a dielectric substrate, the increase in the transmission loss can be suppressed. In the filter arranged with the resonators, the greater the number of the resonators, the better the frequency cutoff characteristics, and frequency resources can be utilized effectively.
As the resonator, various patterns have been used, such as a hair-pin type, a disk type, and a ring type. In those resonator patterns, since the disk type resonator pattern and the ring type resonator pattern can suppress the localization of current as compared to the hair-pin type resonator pattern, they are advantageously highly resistant to voltage. However, when these patterns are stacked in many stages, the filter area is larger than that of the hair-pin type.
When the disk-type resonator pattern is used, a portion of the resonator pattern is cut to be resonated in a dual-mode, whereby the frequency cutoff characteristics per one stack of the resonator pattern can be further improved.
In addition, a method where a dielectric substrate (second dielectric substrate) is overlapped and disposed on the disk-type resonator pattern (resonator pattern formed on the surface of a first dielectric substrate), whereby current concentration can be reduced has been known. Further, a stress dispersing member and a pressure plate are disposed on the second dielectric substrate, and the second dielectric substrate and the resonator pattern are pressurized through the pressure plate, whereby the contact between the second dielectric substrate and the resonator pattern can be made uniform.